Frequency reduction device



Dec. 31, 1940- K. SCHLESINGER 2,227,003

- FREQUENCY REDUCTION DEVICE Filed July '23, 1936 OUTPUT Patented Dec. 31, 1940 PATENT o FFlCE i FREQUENCY REDUCTION DEVICE Kurt Schlesinger, Berlin,

Germany, assignor, by

mesne assignments, to Loewe Radio, Inc., a. corporation of N w York Application July 23, 1936, S erialNo. 92,153 In Germany July 27, 1935 1 Claim. (Cl. 250-36) The problem of producing a frequency which is an integral fraction of a control frequency often arises in the electrical oscillation art, for example in radio telephony and in television.

Frequency dividers using electron tubes are well known. This invention relates to frequency dividers of this kind, and its object is a frequency reduction devise of highest reliability.

, Another object of this invention is to synchronize the lower frequency ft. by the higher control frequency fst without retroaction.

Another object of this invention consists in obtaining the lower frequency in the form of short synchronizing impulses.

In the drawing,

Fig. 1 is a schematic diagram of a connection according to this invention, and

Fig. 2 are curves illustrating the functions of the device of Fig. 1.

20 I The principle of this invention consists in controlling the frequency fa of an ordinary oscillation generator by means of an additional grid connected to the higher frequency source. Consequently a tube having two or more grids is used. Admirably suited for this purpose are normal pentodes having a screen grid and a suppressor grid which are provided with external terminals.

In Fig. 1 the pentode contains a cathode I, a control grid 2, a screen grid 3 with positive bias, a suppressor grid 4 and an anode 5. The screen grid 3 is connected as usual with approximately half the anode battery potential, which is adjusted by means of a potential distributor 6, 1 and is earthed by means of a condenser 8. The bias of grid 4 is adjusted by means of battery I3 in series with resistance l2 and 2|. The reaction coupling between the grid coil 9 and. the oscillatory circuit lO/Il takes place by any of the usual methods, for example inductively. Oscillations of the frequency is. in the anode circuit Ill/ll are generated so long as the distributor grid 4 permits the passage of current to the anode.

According to the invention, there is applied to the distributor grid 4 by way of a condenser 14 the control potential IS, the frequency of which fst is assumed to be an integral multiple of the frequency fa.

In Fig. 2 there is shown the form of the anode current. If the suppressor grid 4 were permanently connected for transmission, for example permanently connnected with the cathode, there would result in the tube an oscillation of the frequency fa. The form of the grid alternating potential of the grid2 controlling this oscillationin the tube is represented in Fig. 2 by the curve I6. The potential prevailing at the suppressor grid 4 has a harmonic frequency of IE, for example double frequency. The same shown in the curve IT. From the co-operation between both oscillations the anode current which occurs may be derived as follows:

In the first half-cycle of ll, which is designated a, the suppressor grid is supplied with a potential permitting current to flow through the tube. There accordingly occurs in this phase an anode current which is designated l8. In the second half-cycle of the suppressor grid potential H, which is designated b, anode current is no longer able to flow, as in this half-cycle the suppressor grid potential is negative. The anode current, therefore, in this range is zero. In the third and fourth half-cycles of the control regions designated by c and (2, however, the anode current is in any case zero, because in this range the control grid 2 is negative. Consequently, for each two full cycles of the control frequency fst there is produced merely one single current impulse at the anode I8.

In addition to this frequency reducing effect there also occurs a synchronizing effect. It will be clear from the above remarks that the oscillation fa of the circuit Ill/ll is only generated if its frequency is subharmonic to the control frequency fst, as otherwise the periods in which the tube would be traversed by current would not coincide with the transmission periods of the suppressor grid 4. i

The frequency of the useful oscillation fa thus generated is accordingly distinctly determined by the control frequency fa. It depends on the tuning of the circuit [0/ H merely insofar as with a detuning of fa taken too far in relation to 1/71., fst is concerned.

The curvature of the potential furnished by the generator is a nearly pure sinusoidal one when taken by coupling tothe coil H].

In many cases, however, there is the desire for a potential, the form of which coincides with the time curve l8 of the anode current. At the same time there should also be adjustable as far as possible the duration time fl of the anode current impulse or of this useful potential. A coupling of this nature may be realized by the introduction of an ohmic coupling resistance I9 in the anode circuit. The resistance I9 should be small compared with the inner resistance of the tube. In the case of pentodes I9 may readily be made to be 10,000-30,000 ohms or more. The potential tapped at E9, possibly by Way of a coupling condenser 20, then supplies the impulse indicated by 18 in Fig. 2. The strength of the impulses may be adjusted by varying the resistance IS. The duration time T of the impulses, in accordance with the invention, may be varied by varying the bias l3 of the suppressor grid 4, generator I remaining at constant potential, or vice versa by varying the amplitude of IE only. Certainly the first method is better, as in this case the generator [5 limiting methods known per se (grid current limitation and anode current limitation of the terminal tube) may be provided which represent efiective means against interfering ripple, hum modulation, etc. It will be obvious that in the case of a more negative bias IS the duration of the transmission phase of 4 becomes shorter and shorter, and the impulse duration time T is accordingly reduced. The greatest duration which time T is capable of attaining is the full half-cycle of the control frequency fst.

If very short impulses are to be generated, there are two possibilities. In the one case the negative bias I3 is increased more and more until merely the extreme positive peak values of the potential variations from generator [5 impulse the suppressor grid. In this connection there is reached a limit of accuracy, as small fluctuations in. the amplitude of already lead to considerable variations in the impulse duration owing to the weak intersection low rate of change of the curve. The second method of obtaining still shorter impulses without encountering these difficulties as regards amplitude consists in selecting as the control frequency a higher harmonic of the useful or desirable frequency, i. e., not the double but the triple or quadruple harmonic. The longest impulse duration is then merely a fraction of the longest duration time T just considered, and the range of still shorter impulse signals is reached without difficulty.

It may be especially pointed out that in the above there are described particular forms of embodiment of the general idea according tothe invention, and that modifications may be made in the present invention without departing from the spirit and scope thereof.

I claim:

A circuit for producing unidirectional impulses at a predetermined rate and of a predetermined duration comprising, an electron discharge tube having a cathode, a first control electrode, a second control electrode and an output electrode, means including an inductance for normally maintaining said first controlelectrode negative with respect to said cathode, a tuned circuit comprising a parallel connected condenser and inductance, means for connecting one terminal of the tuned circuit to the output electrode of said tube, means including a load resistance for maintaining the other terminal of the tuned circuit positive with respect to the cathode, said firstnamed inductance and the inductance of said tuned circuit being mutually coupled, an output circuit coupled across'the cathode and the junction of the loadresistance and the tuned circuit, means including a resistance for normally maintaining said second control electrode negative with respect to the cathode, said negative potentials being of such magnitude as to substantially block the tube, means for applying voltage variations of a fixed frequency between the second control electrode and the cathode, the resonant frequency of the tuned circuit. being approximately one-half the frequency of the voltage variations applied to said second control electrode, said applied voltage variations and the voltage produced by said mutual coupling having such amplitude that said tube is unblocked only when said applied voltage and said produced voltage are each positive, whereby unidirectional impulses of a rate substantially coinciding with the frequency of the tuned circuit and having a duration corresponding to approximately one-fourth the time occupied by one cycle at said frequency are present in said output circuit.

KURT SCI-ILESINGEB. 

